Conventionally, a domed monitoring camera apparatus has a monitoring camera contained in the interior of a dome cover and capturing through the dome cover an image of an object to be monitored. The camera apparatus of this type has been disclosed, for example, in Japanese Patent Laid-Open No. 2004-356669 (FIGS. 1 and 2, and the like).
The conventional monitoring camera apparatus includes mechanisms for back-focus adjustment, zoom adjustment and focus adjustment. In installing the camera, the dome cover is removed, and these mechanisms are manipulated so that back-focus adjustment, zoom adjustment and focus adjustment are done. For back-focus adjustment, the imaging element is moved; and for focus adjustment, the lens is moved. Back-focus adjustment is a type of focus adjustment. After completion of these adjustments, the adjustment mechanisms are fixed, and the dome cover is attached, so that the installation operation is completed.
There are multiple types of dome covers. The type of dome cover varies according to specifications about material, thickness, transmissivity and the like. For example, a smoked cover of a low transmissivity is used so that the monitoring camera inside the cover can be hardly seen from the outside. From a viewpoint of vandalproof, a greater thickness cover is useful.
In the conventional domed monitoring camera apparatus, however, when the dome cover is attached at the final stage of installation operation, the optical path length varies according to the presence/absence of the dome cover and the dome cover specifications; thus the focus position changes slightly, and an out-of-focus state may occur. Examples of dome cover specifications which vary the optical path length include material, thickness and transmissivity.
A purpose of the invention made in the above-mentioned background is to provide a domed monitoring camera apparatus which can reduce a shift or discrepancy in focus dependent on a variation in optical path length caused by a dome cover.